Neural progenitor cells, which build the brain and nervous system, were particularly vulnerable to infection but the study showed "almost all cells in the brain" tested positive for Zika.

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Dr Zhiheng Xu, from the Chinese Academy of Sciences, said: "The most surprising part of this study is that it was mostly neural progenitor cells that got infected in the beginning and mostly neurons that became infected at a later stage.

"However, almost all cell death was found in neurons."

Meanwhile scientists at Washington University have performed the first animal experiments showing how the infection spreads from a pregnant adult to the developing foetus.

It showed Zika preferentially targeted the placenta with viral levels 1,000 times higher than in the blood.

Their study, in Cell, found the virus damaged the placenta and was able to leak over to the foetus.

And a study, published in Nature, used the virus currently spreading in Brazil in animal tests. Again the research team showed mouse brain development was impaired.

Dr Alysson Muotri, one of the researchers in the third study from the University of California San Diego, said: "The media and some of the health agencies were ahead of themselves by concluding the Zika virus was causing microcephaly.

"Experimental and clinical proof that Brazilian circulating Zika virus causes microcephaly is only being presented now."

Dr Derek Gatherer, from Lancaster University, said the findings "add to the weight of evidence that Zika virus is the cause of the apparent spike in microcephaly".

"However, the differences between mouse and human development mean that larger experimental animals that are more similar to humans - such as monkeys - must also be tested. "